Bugfix: large subtitle target duration can result in subtitles not loading as needed #5597
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…ubtitle segment selection Fixes #5595
agajassi
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robwalch
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…on-impacts-segment-selection Bugfix: large subtitle target duration can result in subtitles not loading as needed (cherry picked from commit 7002632)
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This PR will...
Remove the use of target duration in ensuring subtitle segment N-1 is loaded. Instead, find best match for position, then ensure N-1 is loaded.
Improve handling of MPEGTS VTT syncing. Rather than always require initPTS for the subtitle discontinuity sequence, only require it when parsed subtitles include an MPEGTS map value, log when it's missing, and trigger a non-fatal error only when only AV initPTS from lower sequence numbers have been loaded.
Why is this Pull Request needed?
Since target duration is an upper bound of playlist segment durations, and subtitle segments can be very long, using target duration to ensure the last subtitle segment is loaded can lead to subtitle loading starting several segments back. Loading can then idle before reaching the playhead as the subtitle-stream-controller tries to match the media forward buffer length.
The previous subtitle segment must always be loaded since it may contain subtitles that end after the end of the segment which still need to be rendered.
Are there any points in the code the reviewer needs to double check?
Resolves issues:
Checklist